TRPV4-like non-selective cation currents in cultured aortic myocytes.

In this study, we provide evidence of critical changes in the expression of non-selective cation currents (NSCC) during culture in rat aortic myocytes. A selective TRPV4 agonist, 4alpha-phorbol 12,13-didecanoate (4alphaPDD), had little effect on membrane currents and intracellular Ca(2+) (Ca(2+)(i)) in freshly isolated cells from the aorta. In contrast, in cultured aortic myocytes with and without serum, 4alphaPDD at a concentration range between 0.3 and 3 muM effectively elevated Ca(2+)(i), which was abolished in the absence of external Ca(2+). Application of 4alphaPDD to cultured aortic myocytes also activated NSCC, which had a reversal potential of +3 mV. Both of these signals were blocked by ruthenium red (RuR), an effective blocker of TRPVs. Although the expression of TRPV4 mRNA transcript was found in cultured as well as non-cultured aortic myocytes, significant immunoreactivity to TRPV4 protein was only detected in cultured rat aortic myocytes. Moreover, cultured human pulmonary arterial smooth muscle cells (hPASM) had a substantial response to 4alphaPDD, which was susceptible to the removal of external Ca(2+) and application of RuR. These results provide a strong basis for our proposal that endogenous TRPV4 functions as an important regulator of Ca(2+)(i) in vascular myocytes under some physiological and pathophysiological conditions.